But the little girl wasn't the only daughter of Csanadi's friends that he abused.

FBI agents and police identified two others, ranging from ages 4 to 5, in the 25 homemade videos they found in his Newtown home during an April 8, 2011, search. Other videos show young girls as they played on the beach, practiced ballet, sat in shopping carts, sold lemonade and stepped off school buses.

In each the camera lens zooms in on their chest, groin, rear and feet. Agents believe Csanadi made these while traveling around Newtown and nearby towns. They also found 5,100 images of child pornography, some of them displaying sadistic masochism, on his computer.

On Tuesday, Arterton sentenced Csanadi to 20 years in federal prison with the recommendation the U.S. Bureau of Prisons send him to their federal medical facility in Devens, Mass., which has treatment programs for sex offenders. He pleaded guilty on Nov. 2, 2012, to producing child pornography.

The judge said all sentencings are tough, but "this one is terrifying because at the heart of it ... our kids are never safe."

She pointed out the defendant used his friendship with the families to abuse their daughters, leaving the parents completely unaware that anything horrible had happened.

It took the FBI's Childhood Exploitation Task Force, working with Monroe and Newtown police, to uncover the case. An investigator trolling a website determined that Csanadi was downloading child porn. During the search of his home, they discovered the videos.

Csanadi is expected to receive a concurrent 20-year state prison term when he is sentenced in Danbury Superior Court on April 2 for sexual assault and possession of child pornography.

"He is horrified by his conduct," the court-appointed lawyer said. "He spends a lot of his time thinking of the people he hurt."

Thomas recommended Csanadi be sent to the offender program.

"He is a man who needs help," the lawyer said.

Gary Csanadi, the defendant's father, a retired Easton police officer, watched the sentencing. He briefly addressed the judge, and said his son was known for helping others and had turned his life around since kicking a cocaine addiction.

During the sentencing, Thomas told the judge his client was too upset to read a statement. So Thomas read it as three members of one victim's family listened.

"I can't imagine what it was like for a parent to receive a phone call from the police and have their life turned upside down," he wrote. He said he spent nearly every day thinking about what he had done.

Later an aunt of one of the girls addressed the court, telling the judge that Csanadi acted "like a thief in the night" stealing her 5-year old niece's innocence during a sleepover.

"Mr. Csanadi may have a chance to leave prison one day, but my family and I can never walk away from what happened," she said. She looked directly at the seated defendant and told him she was not yet ready to forgive him.

But Csanadi, a stocky man with a shaved head, full beard and mustache, turned to her and apologized.

"I don't know why I do what I did," he later told the judge, adding that he had kicked a cocaine addiction on his own.

"The stuff is on the computer so it's available right there," he said of the pornography. "It's like putting alcohol in front of an alcoholic."

He said he considered treatment, but could not afford the $120 session costs.

Despite his contrition, Patel stood by his description of the defendant.

"He is a monster who crept into the bedrooms of little girls at night," the prosecutor said.

"The monster who visited these girls was not a figment of these little girls' imagination. The monster was real," Patel said. "The monster was David Csanadi."